Showing papers on "Sperm plasma membrane published in 1978"

Mechanisms of activation of sperm and egg during fertilization of sea urchin gametes.

Abstract: Publisher Summary This chapter discusses the fertilization of the sea urchin egg. The metabolic and morphological changes of sea urchin gametes during fertilization are the best characterized of all embryos. In organization, this chapter explains the activation of both gametes, first considering the activation of the sperm upon its contact with egg jelly and the resultant cascade of the events leading to sperm–egg attachment and sperm–egg fusion. It then examines the consequences of sperm fusion with the egg that leads: (1) to the responses, excluding other sperm from fusing with the egg and (2) to the responses that result in the activation of embryonic development. The chapter describes the important roles played by intracellular calcium and cytoplasmic pH in turning on the cell metabolism. In sperm plasma membrane, the receptors interact with some component of the egg jelly or egg surface. This leads to increased Ca2+ content, the induction of membrane fusion, and the acrosomal exocytosis. At the same time, there is an acid efflux, polymerization of internal actin, and exposure of sperm lysins and sperm bindins that are attached to the newly formed membrane of the acrosomal process.

The fine structure of fertilization in the fern Marsilea vestita

Abstract: The ultrastructural details of fertilization in the fern Marsilea vestita, including gamete approach and fusion, the fate of the spermatozoid organelles and the development of a possible block to polyspermy are described. The spermatozoid approaches the egg through layers of mucilage that surround the megaspores. It moves down the neck of the archegonium into the cavity above the egg. In order to reach the egg, it must move through a small hole in the thick wall that lies across the top of the egg. The fusion of the plasma membranes of the gametes results in an outflow of egg cytoplasm into the clear space under the sperm plasma membrane, creating a fertilization cone. All the organelles of the fertilizing spermatozoid, including nucleus, mitochondrion, microtubule ribbon, multilayered structure, and flagellar band, with approximately 150 flagella, enter the egg cytoplasm. The nucleus enters as a condensed rod of chromatin with no nuclear envelope. The chromatin begins to disperse immediately and a new nuclear envelope is formed around the chromatin by egg endoplasmic reticulum. The mitochondrion and the microtubules of the ribbon and flagella are broken down, but the fates of the flagellar band and the multilayered structure have not been determined. After spermatozoid penetration, a new extracellular layer appears above the surface of the egg, beginning in the region of sperm penetration and spreading across the top of the egg. This layer may be important in preventing other spermatozoids from fusing with the egg.